Bøhmer experimented with the concept for a decade, inspired by the simplicity of a solar device invented in 1767 by Swiss physicist Horace-Bénédict de Saussure. The cooker, which consists of two boxes nestled inside each other and topped with Plexiglas to trap the sun’s rays, has evolved from a homemade cardboard contraption to a $6 plastic version that went into mass production this spring.